Chapter 245 Cluster Compounds of Rare-Earth Elements

Abstract: Polynuclear complexes of rare-earth elements characterized by their well-defined, cluster-like core structures are a class of interesting compounds with pleasing molecular structures and potential useful applications. Their synthetic and structural chemistry has been developed rapidly in the last two decades, and a review of this subject is therefore timely. Presented in this chapter are the large number of cluster compounds of rare-earth elements appeared in the literature up to 2008. The discussion of this vast number of cluster species is organized according to the distinct synthetic methods by which they are produced, that is, those obtained under conditions typical of organometallic synthesis and those by deliberate hydrolysis of mononuclear or lower-nuclearity precursors. The common driving force behind the assembly of these cluster species is the inherent tendency of the bulky metal atoms to satisfy their coordination number requirements. The clustering of the individual metal atoms is facilitated by the use of multidentate chelating and bridging ligands, mostly oxygen-based due to the oxophilicity of these unique metal elements. Other heteroatoms, including N, chalcogens, halogens, and H are also frequently found in the coordination sphere, generally in the form of small-unit ligands. With the unabated enthusiasm and efforts from researchers over the world, this cluster chemistry of rare-earth elements has now been developed into a unique research area, and a number of important applications (chemical, biomedical, and materials) have either been realized or envisioned. It is reasonable to predict that activities in this particular direction of chemical research will continue to grow with a high possibility of finding many new species with pleasing structures and useful applications.